(i) Technical Field
A certain aspect of the embodiments discussed herein is related to a semiconductor laser.
(ii) Related Art
An AlGaInP semiconductor laser has attracted attention as a visible light semiconductor laser which emits red light. Some AlGaInP semiconductor lasers have an active layer including a multiple quantum well (MQW) structure.
There has been developed an art to reduce a threshold current in a semiconductor laser of which the active layer has a MQW structure, by introducing a compressive strain or a tensile strain to a well layer (e.g. Japanese Laid-Open Patent Publication No. 07-111367). There has been developed another art to implement a low threshold current operation at high temperature, by introducing a tensile strain to a well layer, and a compressive strain to a barrier layer (e.g. Japanese Laid-Open Patent Publication No. 05-145178).
There is a proposal to introduce one of a compressive strain and a tensile strain to a buffer layer and/or a cap layer when introducing the other of the compressive strain or the tensile strain to an active layer, to obtain stable characteristics by compensating the overall strain of stacked semiconductor layers (e.g. Japanese Laid-Open Patent Publication No. 11-87764).
However, the spectrum half width of PL (photoluminescence) spectrum increases when a tensile strain is introduced to the well layer as described in Japanese Laid-Open Patent Publication No. 07-11367, in the case where the active layer is formed by a MQW structure having a well layer composed of GaInAsP and a barrier layer composed of AlGaInP in order to realize a semiconductor laser that has an emission wavelength between 650 and 700 nm and oscillates in a TM mode.
In addition, when a tensile strain is introduced to the well layer and a compressive strain is introduced to the barrier layer as described in Japanese Laid-Open Patent Publication No. 05-145178, the spectrum half width further increases.
It is an object of the present invention to reduce the spectrum half width.